Circuits may be designed with maximum voltage to load, maximum power to load or, sometimes, no thought to power or voltage transfer. In many situations, maximum power transfer is desirable, as it provides maximum power to the load. It is believed that maximum power transfer may be achieved by matching the impedance of the source to the load (and any intermediate lines or components). Circuits may use a matching network on the source side and load side (see FIG. 1A) or on one side only.
In general, impedance has a complex value; this means that loads (symbolized as Z) generally have a resistance component (symbolized as R) which forms the real part of Z and a reactance component (symbolized as X) which forms the imaginary part of Z. Power transfer theory dictates that for maximum power to be transferred, the source impedance (ZS) should equal the complex conjugate of the load impedance (ZL) such that the following equation holds true: RS+jXS=RL−jXL (see FIG. 1B). As reactance X is variable with frequency, the matching network is generally tuned to one frequency.
Matching the load to the characteristic impedance (Z0) of the transmission line allows reflectionless matching, minimizing reflections from the load. Thus, a transmission line connecting the source and load together would ideally be the same impedance: ZL=Z0=ZS.
While in an ideal world, Z1, Z0 and ZL would be immutable and the same for every product produced, the impedances may be variable due to tolerances and design in manufacturing. Therefore, there is a need to customize each circuit to match impedances in a cost efficient manner.